Apparatus for joining pipe

ABSTRACT

A pipe and sleeve telescoped joint with the pipe and sleeve in sealing engagement and keys embedded in both pipe and sleeve at their interface. The size and number of the keys are calculated from the size and strength of the pipe. The sleeve is sized and its strength selected from the strength of the pipe, and the sleeve ends are shaped to hold the joint circular when it is made. The apparatus includes means for holding the midportion of the sleeve circular when creating the joint, and for cooperating with the sleeve ends to keep them circular. The sealing engagement is created by firing a propellant into a substantially incompressible medium, like water, held by the apparatus in a cavity about the sleeve, and a piston separates the explosive propellant from the pressure medium.

BACKGROUND TO THE INVENTION

This invention relates generally to joining lengths of pipe and moreparticularly concerns methods, structure and apparatus for securing asleeve to a pipe so as to create a pipe splice.

In lieu of welding lengths of pipe to form a pipe line, a method andapparatus for splicing pipe lengths using sleeves to overlap and joinpipe length ends is disclosed in U.S. Pat. No. 4,327,471 entitled"Hydrostatic Pipe Splicing Method" and U.S. Pat. No. 4,330,918 entitled"Hydrostatic Pipe Splicing Apparatus", both assigned to the assignee ofthis application. This technique involves using a short, cylindricalsleeve to span abutted ends of pipe lengths, and then exerting very highpropellant forces to drive the sleeve against the pipe beyond theelastic limit of the sleeve but within the elastic limit of the pipe.Upon dissipation of the propellant force, the pipe elastically returnsand the pipe and sleeve are intimately joined.

A technically successful joint of this kind should ideally be strongerthan the pipe itself in the sense of resisting longitudinal pull-out,and pull-out or separation as a result of bending the pipe line at thejoint. In addition, a commercially successful joint of this kind shouldbe designed to use sleeves and propellant force-creating charges ofminimum size and cost, consistent with achieving the necessary technicalstandards.

OBJECTS OF THE INVENTION

Accordingly, a primary aim of the invention is to provide a sleeve andpipe joint having superior mechanical strength without great overlappingsleeve length. A related object is to provide such a joint that isreliably held in the original circular configuration of the pipe andsleeve so as to maintain structural integrity.

Another object is to provide a joint as characterized above efficientlyusing explosive propellant material to safely and economically developthe required propellant forces to create the joint.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings, in which:

FIG. 1 is a perspective, partially exploded and partially broken away,of an apparatus and structure for creating a pipe joint embodying thepresent invention;

FIG. 2 is a fragmentary longitudinal section of a joint embodying theinvention;

FIG. 3 is an enlarged fragmentary plan of an element of the structureshown in FIGS. 1 and 2;

FIG. 4 is a section taken approximately along the line 4--4 in FIG. 3;

FIG. 5 is an enlarged fragmentary section taken approximately along theline 5--5 in FIG. 1;

FIG. 6 is a section taken approximately along the line 6--6 in FIG. 1;

FIG. 7 is a section taken along the line 7--7 in FIG. 6;

FIG. 8 is a fragmentary section taken approximately along the line 8--8in FIG. 6; and

FIG. 9 is similar to FIG. 8, but shows the parts in a differentoperating position.

DETAILED DESCRIPTION OF THE DRAWINGS

While the invention will be described in connection with preferredembodiments, it will be understood that I do not intend to limit theinvention to those embodiments. On the contrary, I intend to cover allalternatives, modifications, and equivalents as may be included withinthe spirit and scope of the invention as defined by the appended claims.

Turning now to the drawings, there is shown in FIG. 1 an apparatus 10for forming a pipe joint 11 appearing in section in FIG. 2. The joint 11consists of a sleeve 12 and the ends of lengths of pipe 13 and 14telescoped and driven radially together. Keys 15 are embedded in thematerial of the sleeve 12 and the pipe 13, 14 at their interfaces.Preferably, an annular seal 16 is compressed between the ends of thepipe 13, 14 and the sleeve 12 to insure a gas tight joint.

The apparatus 10 includes a chamber 20 for confining a substantiallyincompressible medium with the chamber being defined by end members 21and a cylindrical body 22, sealed between the end members 21, to createan annular cavity 23 surrounding the sleeve 12 and confining the mediumwhen the joint is made. Mounted on the body 22 are an assembly 25 forfiring a propellant into the chamber 20 and a holding assembly 26, whosefunction will be described below.

Operation of the apparatus 10 is generally like that described inabove-identified patent application Ser. No. 228,295. The sleeve 12 isplaced in the cavity 23 and the ends of the pipe 13, 14 are abutted inthe sleeve. The cavity is filled with a substantially incompressiblemedium such as water through a valve 27. A charge of propellant, asopposed to a detonating explosive, is fired into the water medium,causing a pressure build-up exceeding the yield strength of the sleeve12, whereupon the sleeve is, in effect, shrunk onto the pipe ends toform the joint 11.

In carrying out the present invention, for pipe of a given diameter andwall thickness, the sleeve 12, essentially a cylindrical body, is givena diameter that closely fits the diameter of the pipe, a wall thicknessthat is greater than the pipe wall thickness, and a yield strength thatis less than the yield strength of the pipe material. As illustrated,the inner diameter of the sleeve body fits closely the outer diameter ofthe pipe 13, 14, although the reverse can be true for this aspect of theinvention. For example, the pipe could be made of a lower yield strengthmaterial than the sleeve. In that case, the propelled expansion wouldoccur on the inside of the pipe with the yield strength of the pipebeing exceeded and the yield strength of the sleeve not being exceeded.Thus, the softer pipe material would be expanded into the larger sleeve,forming a joint, as contemplated herein.

Referring again to the previous case, by making the yield strength ofthe sleeve less, a propellant force can be calculated that will, in theformation of the joint 11, exceed the sleeve yield strength andpermanently shrink the sleeve while the pipe will, when the propellantforce is dissipated, return to its original size. This produces theinterference fit of the joint. By making the sleeve slightly thicker,the mechanical strength of the joint 11 remains approximately equal tothe mechanical strength of the pipe itself.

Preferably, the sleeve material is metallurgically matched to thematerial of the pipe so as to minimize electrolytic corrosion betweenthe materials. In a practical case, both sleeve and pipe can be weldedcarbon steel pipe.

In accordance with the invention, the keys 15 embedded in the sleeve 12and pipe 13, 14 are dimensioned so as not to enter the pipe surface adistance greater than the allowable discontinuity for rating the pipe,and the size and number of the keys per unit area times the ultimatestrength of the pipe material is less than the unit area force exertedby the propelling force when making the joint. Preferably, the keys 15are formed as a band 30 from which are raised, from both sides, theactual key elements 31 preferably shaped substantially like equilateralpyramids. However, the keys could be machined into the sleeve. Thematerial of the keys 15 must be harder than the materials of the sleeveand pipe, and tungsten carbide is suitable.

To understand the size and spacing relationships referred to above, itwould be helpful to consider some background. Pipe is strength-rated ata thickness 12.5% less than its nominal thickness. Thus, cutting a pipethread less than that dimension will not derate the pipe. The height 32of the key pyramid elements 31 is therefore not greater than 12.5% ofthe thickness of the pipe with which they are to be used. Taking X-42welded steel pipe with a 65/8 inch outer diameter and a 0.188 inch wallthickness, the height 32 should not be over 0.0235 inches.

X-42 pipe has a maximum ultimate strength of approximately 60,000 psi. Akey pyramid element 31 of a given height has a given base area, andhence a given unit force will be required to drive such a key into thepipe material. In the example being discussed, about 24 pounds of forceis needed to drive an equilateral pyramid of that size into X-42 steelpipe. The spacing of the key elements is therefore limited by theindividual key force figure and the unit area force developed by thepropellant in the apparatus 10. A radial pressure of 3,000 psi isavailable for seating the key elements at the pipe yield point. Thistherefore limits the key element spacing to no more than on the order of125 elements 31 per square inch.

A final selection in designing the keys 15, after individual key elementsize and spacing is determined, is how many total key elements should beprovided. Preferably, that number should be such that the projected areaof all key elements longitudinally of the pipe, that is, the height 32taken with a dimension 33, is greater than the pipe cross sectionalarea. Returning to the example being discussed, a key band 30 about 3 to6 inches wide should provide sufficient pyramid element area, with theresult being that the key locked strength of the joint 11 is equal to orgreater than the tensile yield strength of the pipe itself.

As a result of utilizing keys 15 of the size and shape discussed, thejoint 11 is substantially equal to the strength of the pipe itself interms of linear pull-out resistance and resistance to failure uponbending. It will also be apparent from the foregoing that in thedrawings the relative sizes of the keys 15 have been exaggerated forclarity of illustration.

It has been found that the optimal sleeve length, for strength purposesof the resulting joint and to minimize material usage in the sleeve, isbetween two and three times the outer diameter of the pipe. Using thisrange of sleeve dimensions, the resulting joint will resist bendingequivalent with the remainder of the pipe.

Turning to the apparatus 10, the end members 21 are split into two halfsections and clamps 41 are provided for both pulling the sections 21solidly into place about the pipe 13, 14, and drawing the half sectionsagainst the body 22. The sections of the end members 21 and the body 22are formed with tapered surfaces 42 which are cammed by tapered wallgrooves 43 in the clamps 41. Thus, drawing the clamps 41 together usingbolts 44 and nuts 45 both draws the end member 21 half sectionstogether, as well as pulls the end members firmly against the body 22.

An important aspect of the joint 11 is roundness; i.e., keeping thesleeve 12 and pipe 13, 14 truly cylindrical during the making of thejoint 11. In keeping with the invention, the sleeve 12 is formed withtapered ends 47 defining sections of outer cylindrical surfaces, and theend members 21 have tapered surfaces 48 defining sections of innerconical surfaces which are drawn firmly against the sleeve ends 47 asthe clamps 41 are tightened. When the propellant is fired to radiallyshrink the sleeve 12, one result is to slightly expand the sleevelongitudinally, thereby causing the tapered surfaces 47, 48 to forciblycam the sleeve ends into circularity.

As a feature of the invention, the holding assembly 26 acts to engagethe sleeve 12 at a midportion so as to hold its circularity at thisregion. The assembly 26 includes a chamber band 51 secured to the body22 and mounting a plurality of holding pins 52 biased outwardly bysprings 53 but extending into the cavity 23 around the sleeve 12.Surrounding the pins 52 is a cam ring 54, having a camming surface 55for each pin 52, mounted for limited rotation between blocks 56 boltedto the band 51 and the body 22. Two sets of blocks 56 are provided onopposite sides of the body 22 (see FIG. 7). It will be apparent thatupon limited rotation of the ring 54, clockwise in FIGS. 7, 8 and 9, thepins 52 will be driven radially inward to firmly engage the sleeve 12and hold it uniformly circular.

The cam ring 54 is driven by actuators responsive to firing of thepropellant. The actuators include a piston 57 fitted in a chamber 58 ineach of the blocks 56, with the pistons 57 engaging pins 59 mounted inthe ring 54. Passages 61 through the body 22 and blocks 56 connect thebacks of the pistons 57 with the cavity 23 and the water in that cavity.When the propellant is fired, the pressure buildup in the water drivesthe pistons 57 to rotate the cam ring 54 (see FIG. 9) at the same timethat the sleeve 12 is being shrunk, thus maintaining midpointcircularity of the joint 11. Second pins 62 on the cam ring 54 provideforce points for manually returning the ring after firing, and alsocooperate with notches 63 in the blocks 56 to limit ultimate ringrotation.

Another feature of the invention is to provide more controlledpropellant force in the cavity 23 by firing through a piston 70 formingpart of the firing assembly 25. The assembly 25 includes a barrel tube71 containing a chamber member 72 adapted to receive a cartridge 73. Aplug 74 mounting a bolt action firing pin mechanism 75 is threaded intothe end of the tube 71. The piston 70, preferably a thick plastic memberhaving a seal lip 76 and a guiding skirt 77 fitted on the chamber member72, is interposed between the cartridge 73 and the water in the cavity23. Obviously, water is introduced through the valve 27 before thepiston 70, chamber member 72, and plug 74 are sealed in the tube 71 sothat water fills the barrel tube without a trapped air pocket. Firing ofthe cartridge 73 thus directly and immediately drives the piston 70 intothe incompressible medium and generates the required propellant force.

Use of the piston 70 keeps the propellant charge out of the water, whichwould serve as a cooling medium, and permits better gas generation andmore uniform pressure upon firing of the cartridge 73. Also, themaintenance of the pack pressure behind the piston insures ignition ofall of the powder of the cartridge and gives more predictable burningrates. Referring to the example described above, the 9-10,000 psipressure in the cavity 23 can be produced using a cartridge containingabout 16 grams of relatively slow burning number 4756 gun powder.

I claim as my invention:
 1. An apparatus for splicing pipe by sealing asleeve over the ends of adjacent pipe lengths comprising, incombination, a chamber for completely confining a substantiallyincompressible medium about said sleeve, said chamber including a pairof annular end members sized to closely surround said pipe lengths andabut the ends of a sleeve fitted over the ends of adjacent pipe lengths,said chamber also including a cylindrical body sealed between the endmembers and defining an annular cavity surrounding said sleeve, holdingmeans mounted in said body for radial movement to firmly engage saidsleeve intermediate of its ends so as to hold its circularity, means forfiring a propellant into said chamber, and an actuator responsive tosaid firing of a propellant for producing said radial movement of saidholding means.
 2. The combination of claim 1 in which said end membersare split into two half sections, and including clamps for pulling saidsections solidly into place about said pipe lengths.
 3. The combinationof claim 2 in which said clamps cooperate with said cylindrical body todraw said half sections against said body as the sections are pulledinto place.
 4. An apparatus for splicing pipe by sealing a sleeve overthe ends of adjacent pipe lengths comprising, in combination, a chamberfor completely confining a substantially incompressible medium aboutsaid sleeve, said chamber including a pair of annular end members sizedto closely surround said pipe lengths and abut the ends of a sleevefitted over the ends of adjacent pipe lengths, said chamber alsoincluding a cylindrical body sealed between the end members and definingan annular cavity surrounding said sleeve, said sleeve being formed withtapered ends defining sections of outer conical surfaces, said endmembers having circular tapered surfaces defining sections of innerconical surfaces in engagement with the tapered ends of the sleeve,means for introducing a substantially incompressible medium into saidcavity, and means for firing a propellant into said chamber cavity so asto radially shrink said sleeve into sealing engagement with said pipelengths, thereby longitudinally expanding said sleeve and causing saidtapered surfaces to cam the sleeve ends into circularity.
 5. Anapparatus for splicing pipe by sealing a sleeve over the ends ofadjacent pipe lengths comprising, in combination, a chamber forcompletely confining a substantially incompressible medium about saidsleeve, said chamber including a pair of annular end members sized toclosely surround said pipe lengths and abut the ends of a sleeve fittedover the ends of adjacent pipe lengths, said chamber also including acylindrical body sealed between the end members and defining an annularcavity surrounding said sleeve, means for introducing a substantiallyincompressible medium into said cavity, and means for firing apropellant into said chamber cavity so as to radially shrink said sleeveinto sealing engagement with said pipe, said last named means includinga piston interposed between said propellant and said medium so that saidfiring into is through movement of said piston.